FEM calculation of residual stresses induced by laser shock processing in stainless steels

Abstract

Laser shock processing, also known as laser shock peening, generates through a laser-induced plasma, plastic deformation and compressive residual stresses in materials for improved fatigue or stress corrosion cracking resistances. The calculation of mechanical effects is rather complex, due to the severity of the pressure loading imparted in a very short time period (in the ns regime). This produces very high strain rates (106 s−1), which necessitate a precise determination of dynamic properties.Finite element techniques have been applied to predict the residual stress fields induced in two different stainless steels, combining shock wave hydrodynamics and strain rate dependent mechanical behaviour. The predicted residual stress fields for single or multiple laser processes were correlated with those from experimental data, with a specific focus on the influence of process parameters such as pressure pulse amplitude and duration, laser spot size or sacrificial overlay.Among other results, simulations confirmed that the affected depths increased with pulse duration, peak pressure and cyclic deformations, thus reaching much deeper layers (> 0.5 mm) than with any other conventional surface processing. To improve simulations, the use of experimental VISAR determinations to determine pressure loadings and elastic limits under shock conditions (revealing different strain-rate dependences for the two stainless steels considered) was shown to be a key point.Finally, the influence of protective coatings and, more precisely, the simulation of a thermo-mechanical uncoated laser shock processing were addressed and successfully compared with experiments, exhibiting a large tensile surface stress peak affecting a few tenths of micrometres and a compressive sub-surface stress field.

Laser-matter Interaction with Submerged Samples

“…Also, the green light has 100 times longer absorption length in water than 1-µm light, and it can be attractive to use it from the operational point of view 4. Number of pulses to break the sample into nanoparticles To estimate the number of pulses we use the formula for amount of evaporated materials obtained within the peening model 10 . The thickness of ablated material L is related to the plasma size L by eqn 3.1.…”

“…The resultant shock waves 7,8 propagate in both directions from the plasma 9,10 , possibly ablating material [e.g., see Fig 1 from the work of Grigoropoulos and coworkers 11 ]. The water confines the expanding plasma, increasing the pressure and temperature and the plasma lifetime 9,12 .…”

“…and finally we have The system of equations (1.1),(1.2) provides the closed description of the laser plasma interaction in peening experiments 10,14 .…”

Simulation on deforming progress and stress evolution during laser shock forming with finite element method

“…The explicit analysis step is used to solve the dynamic response to LSP, and the following implicit analysis step is applied to making material become stable without long time. Peyre et al (2007) applied ABAQUS to simulate LSP for 12% Cr martensitic stainless steel and 316 L austenitic stainless steel. However, compared with the above mentioned works, he did not carry out the relaxation step using implicit step, and the corresponding relaxation was also accomplished in dynamic analysis step at the cost of long time.…”

Thermal shock behaviors of TiN coatings on Inconel 617 and Silicon wafer substrates with finite element analysis method

“…Finite element analysis (FEA) method has been considered as a useful tool for expecting the change of temperature and stress by thermal and/or mechanical loads since the accurate measurement of the temperature and load in the cutting zone is difficult [14][15][16]. FEA can also be used to determine the stress and temperature distributions in laser-ablated spots [17][18][19].…”